1. Field of the Invention
This invention relates to a process for transforming poultry manure into a material possessing improved properties for use as an ingredient in feed rations for animals.
2. Description of the Prior Art
Poultry manure has been utilized for centuries as a soil enriching material because it contains an advantageous mixture of organic protein, inorganic nitrogen, fiber and minerals. On small farms it is frequently mixed with straw and other litter for use as a soil conditioner.
In large poultry raising operations involving many thousands of caged birds (layers and/or broilers), the freshly voided poultry excreta passes through the wire mesh bottom walls of the poultry cages, and accumulates substantially uncontaminated on the floor, or it is collected in pits designed for this purpose. The excreta can be easily collected, and it is essentially free of other materials, except for feathers.
The disposal of this material, which is collected in large quantities, poses a serious problem to the poultry industry. It is customary to remove the accumulated poultry manure periodically from under the cages and transport it to a disposal area some distance away. After drying and composting the poultry manure for a period of days or weeks, it is then used as a landfill, or it is sold as a soil builder. A major use of poultry manure at the present time is as a soil enriching agent, based on its inherent phosphorus content of 1 to 2 percent and nitrogen content of 3 to 4 percent. None of these uses, however, recover the full potential economic value of poultry manure.
Poultry excreta has a pH of about 6.0 to 7.0 when voided, and it contains from about 70 to 85 percent moisture. It is reported that chicken manure, on an air dry weight basis (about 11 percent moisture), has the following analysis as regards nitrogenous substances:
Range Mean wt.% wt.% ______________________________________ Total protein equivalent 15.2-36.8 28.7 (N + 6.25%) (true protein plus non-protein nitrogen calculated as protein equivalent) True protein 8.1-12.9 10.5
Under present methods of handling poultry manure, within about 24 to 48 hours after excretion, the action of the bacterial flora and the unstable ammoniacal compounds present therein, coupled with the high moisture content, cause the pH to rise to somewhat above 7.0, usually to at least about 8.0 to 9.0. Additional protein breakdown with concomitant release of ammonia occurs, causing the temperature of the manure pile to rise, thereby resulting in an undesirable further protein breakdown.
Over the past several years poultry manure has attracted a considerable amount of interest because of its relatively high protein content. This interest has recently further increased greatly due to the worldwide shortage of protein. State and federal regulatory agencies are presently in the process of establishing regulations regarding the utilization of poultry manure as a supplemental feed ingredient in feed rations for animals, particularly ruminant farm animals such as cattle. The standards being established by the regulations are concerned with, for example, uniformity of product, freedom from toxic levels of materials such as heavy metals, and relative freedom from potentially pathogenic bacteria.
Presently, the accepted procedures for preparing poultry manure for recycling as a feedstuff to animals mostly involve a heating-drying step carried out to remove moisture, to lower the bacteria content, and to convert the manure to a solid state suitable for grinding, screening, or pelleting so that the thus-treated poultry manure can be incorporated with other conventional animal feed ingredients, such as forages and/or cereal grains, to form an animal feed ration. See "Recycling Animal Wastes", by R. Blair et al, Feedstuffs, March 5, 1973. It is very difficult to maintain the stability of the manure at a high pH (about 7.0) during the heating step to achieve removal of potentially pathogenic bacteria and to recover a product whose nutrient value is predictable.